I started on a run/walk program in April 2013, at which point I would have barely been able to run a mile. I was 27 at the time (male). Hadn't really exercised in the 11 years before, save the odd game of squash or tennis - but we are literally talking 2 or 3 time a year max - so essentially 100% sedentary; I was overweight, but admittedly not massive (5'8, probably 161lbs)
Ran my first HM September 2013, running 2:03
Exactly a year later I ran 1:31 on the same course, so a 32min improvement, but still short of sub-90
Eventually ran 1:27 in June 2015, and my PB is now circa 1:22 - but I hope to break 1:20 in the next few months.
The problem with sub-90 is that it became a bit of a mental barrier I think. There was always a tendency to try to run just fast enough to hit the goal, but not too fast to risk blowing up - that's always a dificult balancing act to pull off, when you account for weather, terrain, slightly long course etc. A better bet would have been to get in 1:28 shape first then try to run that; so 1:30 becomes a sort of secondary goal. Hope that makes some sense (it does in my head!).
Training wise I followed Daniels mostly. All standard stuff from his book really; reps sessions early on in the season (such as 200m reps with full recoveries), leading in to longer intervals/hard running (i.e. 6x 3min hard + 2min jog, or 4x 4min hard + 3min jog, etc.).
I always liked the threshold runs, and felt I benefited from them - these could be stuff like 5x 1 mile @ threshold, with 1 min jog (cruise intervals), 3x 2 miles @ threshold, with 2 min jogs etc
Everything else was standard - as many miles as I could comfortably run, and a long run each week. Long runs were not normally much more that 12 or 13 miles; 15 would be absolute max.
Overall, I think the vast VAST majority of my improvement was down to running more; the workouts did help, but most of the initial gains (2:03 to 1:31) were simply down to running more + running regularly.
To my mind; the best thing any new or new-ish runner can do is try to run constantly (i.e. every day, or pretty much every day), for as many miles per week as can be safely handled - don't kill yourself, but if you can consistently run 40mpw with 2 hard days and long run, then stick at that. One mistake I did make was to run 60-70 some weeks, only to find myself back in the 30's a few weeks later - its much better to set a lower goal that you KNOW you can achieve week in week out.
For reference, my mileage was as follows (calendar years) (these are true averages from Strava, weeks within this have varied from as low as zero, to as high as 70 - but it is the average which I believe to be key):
2013: 21mpw (ran 2:03 in Sep-13)
2014: 32mpw (ran 1:31 in Sep-14)
2015: 45mpw (ran 1:27 in Jun-15 + 39min 10k in May-15)
2016: 42mpw (ran 1:22 in Sep-16 + mid-36min 10k also in Sep-16)
Hope all that is of some help, as I was in a similar position to yourself not too long ago. Interesting that my mileage actually dropped last year - hadn't realized that! 40ish mpw sounds so low, but please remember that these are true year-round averages - I could report 50-60 if I decided to leave off quiet periods, holidays, down weeks etc. - but that would be misleading.